In recent years, with the popularity of the camera and the technology maturity of portable compact camera, the demand on the business presentation market is growing, and thus a portable projection screen device is needed.
A known portable projection screen device, such as the prior art shown in “An Improved Structure of a Portable Projection Screen” in Taiwan Publication No. M402443, comprises a first support frame, a second support frame, a projection screen and a linkage, wherein a reel is arranged inside the first support frame. Two sides of the projection screen are respectively connected to the second support frame and the reel. The projection screen is rolled on the reel, and the linkage consists of two links which are pivoted in a cross manner. The left ends of the two links are fixedly pivoted to the left ends of the first and second support frames respectively, and the right ends of the two links are respectively pivoted to the right half parts of the first and second support frames slidably back and forth, so that by means of the linkage the second support frame can be supported. The projection screen can be extended when the linkage is deployed. In reverse, the second support frame can be contracted and the projection screen can be rolled to stow the screen away. Besides, a fixing base and a sliding base which can be latched together are arranged inside the second support frame, and the upper ends of the two links are respectively connected to the fixing base and the sliding base so that the sliding base can be driven by the upper end of one of the links to be latched with the fixing base when the linkage is fully deployed, so as to achieve an effect of maintaining the fully deployed state of the linkage.
Although the prior art realizes a portable projection screen which can be deployed and retracted, the projection screen is not vertically adjustable, cannot be fixed at an intermediate position, and thus the projection screen has only one deploying size. Each time the projection screen is deployed, the sliding base must be latched with the fixing base to maintain the expanding state. After many repetitions of latching, the sliding base and the fixing base may malfunction or may be damaged. This is undesired by people seeking a product with long service life. Further, in the prior art, when the projection screen is to be retracted, the latching state between the sliding base and the fixing base first must be released, which may be troublesome. In addition, since prior art screens are not continuously adjustable, there is a risk that the second support frame would fall freely, injuring a user's hands. If the sliding base is not latched firmly with the fixing base, or if the user's hands fail to firmly hold the second support frame when the second support frame is raised to deploy or lowered to fold, injury also may result.